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PH-EP-2012-214

(Submitted on 03 Aug 2012)

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Abstract

A search for the decay $B^0_s\rightarrow J/\psi K^{*0}$ with $K^{*0}
\rightarrow K^-\pi^+$ is performed with 0.37 fb$^{-1}$ of $pp$ collisions at
$\sqrt{s}$ = 7 TeV collected by the LHCb experiment, finding a $\Bs \to J\psi
K^-\pi^+$ peak of $114 \pm 11$ signal events. The $K^-\pi^+$ mass spectrum of
the candidates in the $B^0_s$ peak is dominated by the $K^{*0}$ contribution.
Subtracting the non-resonant $K^-\pi^+$ component, the branching fraction of
\BsJpsiKst is $(4.4_{-0.4}^{+0.5} \pm 0.8) \times 10^{-5}$, where the first
uncertainty is statistical and the second systematic. A fit to the angular
distribution of the decay products yields the \Kst polarization fractions $f_L
= 0.50 \pm 0.08 \pm 0.02$ and $f_{||} = 0.19^{+0.10}_{-0.08} \pm 0.02$.

Fit to the $K\pi$ mass spectrum for (a) $ B ^0 \rightarrow J/\psi K \pi$ events, and
(b) $ B^0_s\rightarrow J/\psi K \pi$ events. The $ B^0_{(s)}\rightarrow J/\psi K \pi$ yields in each bin
of $K\pi$ mass are determined from a fit to the
$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K \pi$ mass spectrum. The pink dashed-dotted line represents the
$ K ^{*0}$ , the red short-dashed line is the {S-wave} and the black dotted line is
the $K^{*}_2(1430)$. The black solid line is their sum.

Projections of the fit in $M_{J/\psi K\pi}$ and in the angular
variables for the mass range indicated by the two dashed vertical lines in the
mass plot. The red dashed, pink long-dashed, and blue dotted lines represent
the fitted contributions from $ B ^0 \rightarrow J/\psi K^{*0}$ , $ B^0_s\rightarrow J/\psi \overline{ K }{} ^{*0} $ and background. The black
solid line is their sum.